The SORT robot, designed by startup Kindred, uses artificial intelligence to decide which object would be best to pick, avoiding overlapping items and dropping those whose bar codes can’t be read on the first round. When the robot can’t figure out how to grasp an item, it calls workers at Kindred’s Toronto office who take over and do it remotely.

The number of completely autonomous “picks” has increased fourfold since the second phase of the pilot began in April. The SORT now works at about the same pace as human workers on average, and has peak speeds that outperform humans—without taking breaks.

“When you see a machine sitting here, this would be four people working across four shifts,” said Kevin Kuntz, Gap Inc.’s senior vice president of global logistics fulfillment. “That’s the benefit. It works all the time.”

Gap still doubles or triples its usual workforce during its busy sales season, but automation including the SORT robot means it no longer has to hire six times as many workers, Mr. Kuntz said.